The main character, a high school teacher and the youngest son of the Itoshiki family. He always wears a hakama and kimono abroad, preferring flippant casual western clothing in his hometown. When his name is written horizontally it resembles zetsubou ("beyond hope" or "despair"), befitting his extremely negative, paranoid and pessimistic attitude.

He often shouts "I'm in despair!" and attempts suicide several times, though rarely with serious intent. Most of the main girls seem to have feelings for him but only because they misunderstand what he said to each of them (during the episodes introducing them).

His negative personality started blossoming when he was in his first year of high school when he 'accidentally' joined a 'Negative' club. He is based upon the main character from Dazai Osamu's No Longer Human, which is both Nozomu's and the author's favorite novel.

It is revealed that due to countless attempts of suicide, Nozumu is constantly living on the border between life and death. This allows him to see the dead.